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Abstract:Division of the mediastinum into compartments is used to

help narrow the differential diagnosis of newly detected mediastinal

masses, to assist in planning biopsy and surgical procedures, and to

facilitate communication among clinicians of multiple disciplines.

Several traditional mediastinal division schemes exist based upon

arbitrary landmarks on the lateral chest radiograph. We describe a

modern, computed tomography-based mediastinal division scheme,

which has been accepted by the International Thymic MalignancyInterest Group as a new standard. This clinical classification defines a

prevascular (anterior), a visceral (middle), and a paravertebral (poste-

rior) compartment, with anatomic boundaries defined clearly by com-

puted tomography. It is our intention that this definition be used in the

reporting of clinical cases and the design of prospective clinical trials.

Key Words:Mediastinum, Compartments, CT.

(J Thorac Oncol.2014;9: S97S101)

The mediastinum is an intricate segment of the thorax thatcontains vital intrathoracic structures such as the heart and

great vessels, trachea and main bronchi, esophagus, thymus,venous and lymphatic structures, and nerve tissue. As dividingthe mediastinum into specific compartments aids in the genera-tion of differential diagnoses at initial presentation and facilitatessurgical treatment plans, several different classification systemshave been developed in the past by anatomists, clinicians, andradiologists. However, these existing schemes represent arbitrarynonanatomical divisions of the thorax based largely on the lateral

chest radiograph. The lack of a computed tomography (CT)-centric scheme is problematic as the diagnosis, work-up (includ-ing biopsy approach), and formulation of treatment strategies arenow determined by CT findings and not by chest radiography.

The International Thymic Malignancy Interest Group(ITMIG) has an established process to develop internationalstandards in the realm of mediastinal disease; this method wasapplied to create a practical CT-based division of the medias-tinum. First, ITMIG analyzed the existing literature regardingmediastinal compartments. Particular attention was paid to amediastinal classification system based on transverse CT imagesrecently proposed by the Japanese Association for Research ofthe Thymus (JART) in order to facilitate differential diagnosis ofmediastinal lesions.1This model, which was derived from a ret-rospective analysis of 445 nonconsecutive pathologically provenmediastinal lesions, divides the mediastinum into four compart-ments. Based on discussions with experts in the field, ITMIGhas modified the JART model; following the ITMIG process forstandards, this proposed modification was extensively reviewedand subsequently adopted by ITMIG members. In this article,we describe this new, anatomically based mediastinal compart-

ment system that can be used to accurately localize mediastinallesions and formulate focused differential diagnoses.

METHODSThe process used in the development of this document

was designed to represent a consensus within the communityof clinicians and researchers interested in the divisions of themediastinum and mediastinal diseases. A multidisciplinarygroup of 45 experts in thoracic surgery, oncology, diagnosticradiology, and pathology was surveyed regarding their prefer-ence for a 3-compartment or a 4-compartment model. A coreworkgroup (E.M.M., B.W.C., and F.C.D.) analyzed this data,reviewed the existing literature regarding mediastinal classi-

fication schemes, and drafted a proposed CT-based compart-ment model. This proposal was then refined by an extendedworkgroup (N.T., F.Y.B., M.L.R., J.N., and P.M.B.). The docu-ment was distributed to all members of ITMIG for commentsand revised again. The final document was approved andadopted as an ITMIG standard by ITMIG members.

MEDIASTINAL COMPARTMENTS:A MODERN SYSTEM

BackgroundNumerous methods for classifying the mediastinal

compartments have been published, the most common of

Copyright 2014 by the International Association for the Study of LungCancerISSN: 1556-0864/14/0909-0S97

A Modern Denition of Mediastinal Compartments

Brett W. Carter, MD,* Noriyuki Tomiyama, MD, Faiz Y. Bhora, MD,Melissa L. Rosado de Christenson, MD, Jun Nakajima, MD,Phillip M. Boiselle, MD,

Frank C. Detterbeck, MD,# and Edith M. Marom, MD*

*Department of Diagnostic Radiology, The University of Texas MD AndersonCancer Center, Houston, TX; Department of Radiology, Osaka UniversityGraduate School of Medicine, Osaka, Japan; Department of ThoracicSurgery, St. Lukes-Roosevelt Hospital Center, Columbia UniversityCollege of Physicians and Surgeons, Division of Thoracic Surgery,

Continuum Cancer Centers of New York, New York, NY; Department ofRadiology, The University of Missouri-Kansas City, Saint Lukes Hospitalof Kansas City, Kansas City, MO; Department of Thoracic Surgery,Graduate School of Medicine, University of Tokyo, Bunkyo-ku, Tokyo,Japan; Department of Radiology, Beth Israel Deaconess Medical Center,Boston, MA; and #Division of Thoracic Surgery, Department of Surgery,Yale University School of Medicine, New Haven, CT.

Disclosure: The authors declare no conflict of interest.Address for correspondence: Brett W. Carter, MD, Department of Diagnostic

Radiology, The University of Texas MD Anderson Cancer Center, 1515Holcombe Blvd., Unit 1478, Houston, TX 77030. E-mail: [email protected]

ITMIG DEFINITIONS AND POLICIES
mailto:[email protected]:[email protected]:[email protected]:[email protected]


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which include the Shields classification scheme2 used inclinical practice and the traditional, Fraser and Pare, Felson,Heitzman, Zylak, and Whitten models38 used in radiologicpractice. However, differences in terminology and methodsbetween these schemes have resulted in confusion amongphysicians. Additionally, because traditional models are based

on the lateral chest radiograph, some mediastinal abnormali-ties cannot be reliably localized to a specific compartment, asconsiderable overlap exists.

As mediastinal lesions are optimally evaluated withcross-sectional imaging techniques, principally CT and MRI,accurate localization of the origin of the lesion and the extentof disease are crucial. It is only recently that a CT-based clas-sification scheme for division of the mediastinal compart-ments has been proposed.1A universally adopted scheme isparticularly relevant because a growing number of mediasti-nal abnormalities are detected by CT studies performed forscreening and other purposes.9Therefore, consensus regard-ing a standardized method for dividing the mediastinum into

specific compartments based on CT imaging is necessary inorder to appropriately describe mediastinal lesions and formu-late relevant differential diagnoses.

Number of CompartmentsIn constructing a CT-based definition of mediastinal

compartments, one of the most important decisions involvedthe number of specific compartments to include in the sys-tem. Classification schemes have traditionally divided themediastinum into three or four compartments, depending onwhether a superior mediastinal compartment is distinguishedor not. Most 4-compartment models include superior, anterior,middle, and posterior divisions, whereas the 3-compartment

models describe only anterior, middle, and posterior divisions.Both models have strengths and weaknesses.

Advantages of a 4-compartment CT model include thesimilarity to established anatomic and radiologic 4-compart-ment models, the efficacy of such a system as demonstrated bythe CT-based classification system proposed by JART, and thefact that the majority of thyroid goiters are typically locatedwithin the superior mediastinum. Disadvantages of a 4-com-partment CT system include increased complexity, the generalperception that most clinicians and radiologists do not use theexisting 4-compartment schemes,10 and several nonanatomicfeatures. For example, the division between the superior andinferior (anterior, middle, and posterior) compartments is com-

pletely artificial and nonanatomic, as infectious and inflamma-tory processes, and tumors may freely spread to both sectionswithout being restricted by fascial planes. Furthermore, pos-terior neurogenic tumors do not respect this arbitrary division.This nonanatomic boundary makes implementation and dis-semination of any 4-compartment model difficult.

Advantages of a 3-compartment CT model includethe similarity to the published anatomic, clinical, and radio-logic 3-compartment models currently used, less complicateddesign, and the fact that specific compartmental boundariesare established along true anatomic planes. The primary dis-advantage of the 3-compartment model is that merging thesuperior and anterior mediastinal compartments may not

result in adequate separation of entities that occur in each ofthese locations. However, the benefit of distinguishing a sepa-rate superior compartment arises primarily by separating thy-roid goiters from other anterior mediastinal tumors.1In actualpractice, this is rarely a clinical dilemma since a thyroid goitercan usually be reliably identified on CT. Thus, in the era of

CT, the advantage of having a separate superior mediastinalcompartment decreases.

Among the surveyed multidisciplinary group of 45experts, 72% preferred the 3-compartment model, 23% pre-ferred the 4-compartment model, and 5% did not have a prefer-ence. Reasons why the participants chose one model over theother included optimal distinction of disease entities in 67%,similarity to what they currently use in 63%, because it is moreanatomic in 53% and because it is easier to use in 48%.

Based on this feedback given by this group, a 3-com-partment model was selected as the backbone for the CT-basedclassification scheme proposed by ITMIG.

Localization of Mediastinal AbnormalitiesBecause establishing a presumptive clinical diagnosis is

extremely valuable in guiding the work-up and treatment of apatient with a mediastinal mass, having a reliable way to iden-tify the origin of a lesion is important. Sometimes very largemediastinal lesions extend from one compartment to another,making it hard to identify the site of origin. There are twotools that are helpful in deciphering the compartment fromwhich the tumor originated. The first is the center method.In this method, the center of a mediastinal lesion (defined asthe center point of the lesion on the axial CT image showingthe greatest size of the lesion) localizes the abnormality to aspecific compartment. In the JART study, this method resulted

in classification of all 445 mediastinal masses to specific com-partments.1 The second tool is the structure displacementtool. Very large mediastinal masses can displace organs fromother compartments, usually those that abut the compartmentfrom which the tumor originated. For example, a very largeanterior mediastinal mass may displace organs of the middlemediastinal compartment such as the trachea or the heart pos-teriorly. ITMIG recommends that both of these methods beused to localize mediastinal abnormalities on CT scans.

ITMIG Definition of Mediastinal CompartmentsWe propose a 3-compartment model of the mediastinum

including prevascular (anterior), visceral (middle), and para-

vertebral (posterior) compartments, as mediastinal compart-ment boundaries and the anatomic structures they contain canbe readily identified on CT (Fig. 1 and 2).

In the proposed CT-based classification system, we rec-ommend the following boundaries of the prevascular compart-ment: (1) superiorlythe thoracic inlet, (2) inferiorlythediaphragm, (3) anteriorlythe sternum, (4) laterallytheparietal mediastinal pleura, and (5) posteriorlythe anterioraspect of the pericardium as it wraps around in a curvilinearfashion (thus any vessels contained within the pericardiumare located in the middle mediastinum) (Table 1). Based onthese landmarks, the major contents of the prevascular com-partment include the thymus, fat, lymph nodes, and the left


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brachiocephalic vein. Therefore, the most common massesin the prevascular compartment include thymic abnormali-ties (cysts, hyperplasia, and malignancies such as thymoma,thymic carcinoma, and neuroendocrine tumors); germ cellneoplasms; lymphoma; metastatic lymphadenopathy; andintrathoracic goiter (Fig. 3A). Posterior and inferior dis-placement of the vessels described as the posterior bound-aries of the compartment by these lesions may be used to

assign these mediastinal abnormalities to the prevascularcompartment.

The visceral compartment is defined by the followingboundaries: (1) superiorlythe thoracic inlet, (2) inferiorlythe diaphragm, (3) anteriorlythe anterior aspect of the peri-cardium (which envelops the distal aspect of the superior venacava, the proximal aspect of the ascending aorta and lateral rimof the aortic arch, and the intrapericardial pulmonary arteries),and (4) posteriorlya vertical line connecting a point on thethoracic vertebral bodies 1 cm posterior to the anterior marginof the spine (visceralparavertebral compartment boundaryline) (Table 1). This vertical line was selected as the posteriorboundary of the visceral compartment and the anterior bound-

ary of the paravertebral compartment because most neoplasmsin the latter compartment are neurogenic tumors that arisefrom dorsal root ganglia/neurons adjacent to the intervertebralforamina. The major contents of the visceral compartment fallinto two main categories: (1) a vascular category (i.e., heart,superior vena cava, ascending thoracic aorta, aortic arch, anddescending thoracic aorta, intrapericardial pulmonary arteries,and the thoracic duct) and (2) the trachea, carina, and esopha-gus, which share an embryological origin (the endoderm) aswell as lymph nodes. In the JART description, the middlecompartment did not include the heart and great vessels1; incontrast, we suggest that all structures within the pericardiumbe included in the visceral compartment. We consider struc-

tures such as the extrapericardial pulmonary arteries and veinsto be pulmonary and not mediastinal structures. The majorityof abnormalities in the visceral compartment include lymph-adenopathy (related to lymphoma or metastatic disease), fore-gut duplication cysts, tracheal lesions, and esophageal tumors(Fig. 3B). Additionally, lesions of the heart, pericardium (e.g.,pericardial cyst), and great vessels (e.g., aortic aneurysm) mayalso be encountered in this compartment (Fig. 3C).

The paravertebral compartment is defined by the fol-lowing boundaries: (1) superiorlythe thoracic inlet, (2)inferiorlythe diaphragm, (3) anteriorlythe visceral com-partment, and (4) posterolaterallya vertical line along theposterior margin of the chest wall at the lateral aspect of the

FIGURE 1. Coned-down contrast-enhanced axial CT images slightly below the aortic arch (A), at the level of the left pulmonaryartery (B), and at the level of the left atrium (C) demonstrate the proposed classication scheme. Red, prevascular compartment;green, visceral compartment; yellow, paravertebral compartment; blue line, visceralparavertebral compartment boundary line.

FIGURE 2. Sagittal reformatted image from contrast-enhanced CT demonstrates the proposed classicationscheme. It is important to note that the prevascular compart-ment wraps around the heart and pericardium in the visceralcompartment. Red, prevascular compartment; green, visceralcompartment; yellow, paravertebral compartment; blue line,visceralparavertebral compartment boundary line.


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TABLE 1. ITMIG Denition of Mediastinal Compartments

Compartment Boundaries Major Contents

Prevascular Superior: Thoracic inletInferior: DiaphragmAnterior: SternumLateral: Parietal (mediastinal) pleural reflections; lateral margin of the bilateral

internal thoracic arteries and veins, and superior and inferior pulmonary veinsPosterior: Anterior aspect of the pericardium, which lies along the anterior margin

of the superior vena cava, ascending aorta, and the lateral rim of the aortic arch,superior and inferior pulmonary veins

ThymusFatLymph nodesLeft brachiocephalic vein

Visceral Superior: Thoracic inletInferior: DiaphragmAnterior: Posterior boundaries of the prevascular compartmentPosterior: Vertical line connecting a point on each thoracic vertebral body at 1 cm

posterior to its anterior margin

Nonvascular: Trachea, carina, esophagus, lymph nodesVascular: Heart, ascending thoracic aorta, aortic arch,

descending thoracic aorta, superior vena cava,intrapericardial pulmonary arteries, thoracic duct

Paravertebral Superior: Thoracic inletInferior: DiaphragmAnterior: Posterior boundaries of the visceral compartmentPosterolateral: Vertical line against the posterior margin of the chest wall at the

lateral margin of the transverse process of the thoracic spine

Paravertebral soft tissues

FIGURE 3. Representative examples of mediastinal masses. (A) Coned-down contrast-enhanced axial CT image shows a large het-erogeneous mass (M) in the prevascular compartment consistent with a biopsy-proven thymoma. Note the posterior displacementof the heart and great vessels, conrming its anterior location. A left pleural effusion (E) and right pleural nodules (arrows) repre-sent pleural dissemination. (B) Coned-down contrast-enhanced axial CT image shows a low attenuation mass (M) located betweenthe left atrium and the thoracic spine, conrming its location in the visceral compartment. Endoscopic biopsy revealed esophagealcancer. (C) Coned-down contrast-enhanced axial CT image shows a low attenuation mass (M) located within the left atrium in thispatient with an angiosarcoma. The intracardiac location of this lesion conrms its location in the visceral compartment. (D) Coned-down contrast-enhanced axial CT image shows a large mass (M) with calcications in the left mediastinum. The mass displacesorgans of the visceral compartment such as the heart anteriorly and the central portion of the lesion is localized to the paraverte-bral region; thus the origin of this mass is in the paravertebral compartment. CT-guided biopsy demonstrated ganglioneuroma.


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transverse processes (Table 1). As the major contents of theparavertebral compartment include the thoracic spine andparavertebral soft tissues, most abnormalities in this regionare neurogenic tumors arising from the dorsal root ganglia/neurons adjacent to the intervertebral foramina (Fig. 3D).Additionally, paravertebral lesions related to infection and

trauma may also be encountered in this compartment.

CONCLUSIONThe proposed mediastinal division is based on bound-

aries identifiable on routine cross-sectional imaging, princi-pally CT, and at surgery. Because of the increasing number ofpatients in whom a mediastinal abnormality is first discoveredon CT, and because of its simplicity, this division should bestraightforward and can be adopted by clinicians in multipledomains. We anticipate that this system will improve tumorlocalization, help generate a focused differential diagnosis,and assist in tailoring biopsy and treatment plans. In addition,this universal system should facilitate communication among

surgeons, oncologists, radiologists, and pathologists world-wide, with the added benefit of ultimately helping to createmeaningful prevalence studies across institutions.

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a modern definition of mediastinal compartments.6 (1)

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